mwh: Well, from the documentation that came
with the tibook (I had to hunt that one down :-), it says "If
your battery runs low while you are working, you can put
your PowerBook to sleep and replace the battery with a
charged one. The internal backup battery provides enough
power to maintain the contents of RAM for one minute while
you change the battery."
So there you go ;-)

(Hi, rest of advogato! I've started fostering some open
source OS X apps on freshmeat.net for people
interested. So far there's Fire.app, and hopefully more to
come.)